The present invention relates in general to processing speech signals and, in particular, to methods and apparatus for reducing noise associated with an electrical speech signal.
Speech signals are often degraded by the presence of noise. For example, the difficulty a speech recognition system has in recognizing words in a speech signal is increased by the presence of background noise. Further to this example, an automatic speech recognition system in a cellular telephone must overcome the presence of road noise, factory noise, etc. Currently, many attempts to improve the robustness of the front-end portion of automatic speech recognition systems against additive noise distortion are being made. In general, all of these attempts are based on the ides of estimating and reducing the noise in the frequency domain. For example, spectral subtraction or Wiener filtering made be used to reduce noise in the frequency domain. However, these techniques have reached a performance plateau and additional processing techniques are required.